WEDNESDAY, Jan. 19 (HealthDay News) -- Across the United States, suicide risk appears to be significantly higher among people who live in higher altitudes, new research suggests.
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The latest observation seems to confirm the findings of previous research that unearthed a complex and as-yet not fully explained relationship between higher than average suicide rates and residency in higher elevations.
"Once you get to somewhere between 2,000 and 3,000 feet, you start seeing the suicide rates increase," explained study author Dr. Barry E. Brenner, a professor of emergency medicine and internal medicine, as well as program director, in the department of emergency medicine at University Hospital Case Medical Center in Cleveland. "The correlation is very, very, very high, and it happens in every single region of the U.S."
"And yet as you go up in altitude the overall death rate, or all-cause mortality, actually decreases," Brenner noted. "So, the fact that suicide rates are increasing at the same time is a really significant and really striking finding."
Brenner and his colleagues discuss their results in the Jan. 18 online issue of High Altitude Medicine & Biology.
The authors noted that data collected earlier this decade indicates that, globally, suicide is the 14th most common cause of death, amounting to 1.5 million fatalities every year.
Brenner's new evidence of a linkage between suicides and high altitudes stem from an analysis of two decades worth of mortality data (1979-1998) obtained from the U.S. Centers for Disease Control and Prevention.
The CDC figures covered deaths that occurred in all 2,584 counties across the United States in that timeframe. At the same time, the authors obtained countywide elevation statistics from the U.S. Geologic Survey.
The research team determined that over the course of the 20-year period, suicides accounted for 1.4% of all American deaths, with an average county-wide suicide rate of 14 out of every 100,000 residents.
Even after adjusting for traditional risk factors such as age, race, household income, population density, and gender, the authors found that suicide rates (whether involving a firearm or not) were significantly higher than average in those counties with higher altitudes.
Even after adjusting for greater isolation, lower income and greater access to firearms, the findings remained statistically significant, the authors said.
In contrast, those same locales defined by relatively high topography were not home to the highest rates of death due to any and all causes. In fact, higher altitude counties actually registered lower than average death rates due to all causes.
This latter finding actually highlighted the strength of the apparent connection between suicide risk and high altitudes, the research team said.
For the time being, Brenner and his colleagues cautioned that attempts to explain the association are "speculative."
"It may be related to obesity levels and sleep apnea that may be more common in higher altitudes," Brenner suggested. He and his colleagues also noted that hypoxia -- inadequate oxygen supply to the body's cells and tissues -- is more common at high altitudes, and is thought to increase mood disturbances, especially among emotionally unstable patients.
"It could be that hypoxic environments may lead to higher levels of depression or higher tendencies among the depressed to take suicidal action," he said. "It's an area that is rife for further investigation."
Meanwhile, the research team suggested that their findings might help draw attention to residents of higher elevations who could benefit from relocation to lower altitudes and/or suicide monitoring and prevention services.
Last fall, Dr. Perry F. Renshaw, a professor of psychiatry at the Utah School of Medicine and an investigator with the Utah Science Technology and Research (USTAR) initiative, led a similar study that reported a correlation between high altitudes and higher suicide rates.
His work -- published in the American Journal of Psychiatry -- also crunched 20 years' worth of data provided by the CDC. That effort revealed that nine states in the so-called "Intermountain West" region of the country (Montana, Idaho, Wyoming, Utah, Colorado, Nevada, New Mexico, Arizona and Oregon) all ranked among the top 10 states in the nation in terms of suicide rates.
Noting that these states have some of the highest altitudes in the country, Renshaw's analysis concluded that high altitude seems to be an independent risk factor for suicide, particularly among people already prone to depression and mood disorders.
"So my take on this new study is that it's wonderful that independently of each other we got to the same point," Renshaw said. "Because within the suicidology world, we are always concerned that we are missing something, or that this isn't relevant. But here, this group is probably even more methodologically sophisticated than we are, so the fact that we did much the same thing and they have replicated our finding is a very good thing."
"I'm also not surprised that they found that suicide rates differ from the overall mortality experience in high altitude places," he added. "Because many people do seem to adapt quite well to living in a higher altitude, and there's something about committing suicide that's clearly very different from mortality risk."
"But for those people with pre-disposing factors to suicide, like depression and emotional distress, there really appears to be something quite pernicious about living at a higher altitude," he concluded. "And this confirming finding puts us all in a better position to further explore the subject and get a better understanding of what's going on."
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SOURCES: Barry E. Brenner, M.D., Ph.D., professor, emergency medicine and internal medicine, and program director, department of emergency medicine, University Hospital Case Medical Center, Cleveland; Perry F. Renshaw, M.D., Ph.D., professor, psychiatry, Utah School of Medicine, and investigator, Utah Science Technology and Research (USTAR) initiative; January 2011 High Altitude Medicine & Biology, online